Engineering our climate to stop global warming may seem like science fiction, but at a recent National Academy of Sciences meeting, scientists discussed some potential geoengineering experiments in earnest.

Climate researcher Ken Caldeira was skeptical when he first heard about the idea of shading the Earth a decade ago in a talk by nuclear weapons scientist Lowell Wood.Caldeira conducts research on climate and carbon cycles at the Carnegie Institution at Stanford University. During the past decade, he said, talk about this idea has moved from cocktail parties to very sober meetings, like the workshop this week put on by the National Academy of Sciences.

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"Frankly, I'm a little ambivalent about all this," he said during a break in the meeting. "I've been pushing very hard for a research program, but it's a little scary to me as it becomes more of a reality that we might be able to toy with our environment, or our whole climate system at a planetary scale."

Attempting to geoengineer a climate fix raises many questions, like when you would even consider trying it. Caldeira argued that we should have the technology at the ready if there's a climate crisis, such as collapsing ice sheets or drought-induced famine. At the academy's meeting, Harvard University's Dan Schrag agreed with that — up to a point.

"I think we should consider climate engineering only as an emergency response to a climate crisis, but I question whether we're already experiencing a climate crisis — whether we've already crossed that threshold," Schrag said.

Photo shows Mount Pinatubo in the Philippines in 1991. Eruptions like this send sulfate particles into the air. These
particles reflect part of the sun's radiation and have a cooling effect
on the Earth. Scientists are debating whether spraying tiny particles
into the stratosphere could help combat global warming.